1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a cathode in a cathode ray tube (CRT).
2. Background of the Related Art
Referring to FIG. 1, in general, the CRT is provided with a panel 1 having a coat of fluorescent film, a shadow mask 4 fitted to an inside of the panel, and a funnel 2 having a neck tube 3 of a funnel form in rear. There is an electron gun 5 built in the neck tube 3 having a cathode 10 therein. Thermal electrons from the cathode 10 are focused to form an electron beam, which is controlled by a magnetic field from a deflection yoke 7 around an outer part of the neck part. The color for the CRT is then selected at the shadow mask 4 for illumination by the electron beam, which lands on a preset location of the fluorescent film screen and causes the fluorescent film to emit a light and display a picture.
Referring to FIG. 2, the cathode 10 is provided with an emission layer 12, a base metal 14, a heater 16, a sleeve 20, and a holder 18. The emission layer 12 is primarily made of an alkali earth metal carbonate, such as barium carbonate BaCO3, strontium carbonate SrCO3 or calcium carbonate CaCO3 The emission layer 12 is usually in an acicular form of fine powder with a long axis of approximately 8 xcexcm, and a short axis of approximately 0.5 xcexcm which can be spray coated on the base metal 14. The base metal 14 is primarily made of nickel with a small amount of a reducing agent, such as magnesium or silicon, for promoting reduction of the emission layer 12 and supporting the emission layer 12.
The heater 16 has a resistance wire primarily composed of tungsten (W) with a coat of alumina (Al2O3) thereon as an insulating layer. For generating heat, the sleeve 20 is primarily composed of Nixe2x80x94Cr. The holder 18, which supports the base metal 14 and transmits heat from the heater 16 to the base metal 14, is primarily composed of an alloy of nickel for holding the sleeve 20.
The cathode in the CRT emits thermal electrons to form an electron beam. Meanwhile, the heat from the heater 16 is transmitted to the emission layer 12 by conduction and radiation through the sleeve 20.
The picture presentation time lag is the amount of time required from the application of power to the heater 16 to the eventual presentation of a picture on the screen. This lag depends upon the heater power consumption and thus the heater power required for regular operation of the CRT. It is important that the picture presentation time lag is made shorter while the heater power consumption is reduced in order to optimize the efficiency of the display. In other words, minimizing the picture presentation time lag can be achieved by transmitting the heat from the heater to the emission layer within a minimal time period to therefore minimize the heat loss at the heater 16.
Therefore, in order to minimize the heat loss, a reductive heat treated sleeve 20 for reducing a heat loss from radiation is often employed. However, the use of such a sleeve 20 has often led to a long picture presentation time lag as the sleeve has a long time period of heat storage during the heat conduction.
FIG. 2A illustrates a related art method for reducing heat loss, which includes blackening only an inside surface 20a of the sleeve 20, as described in JP laid open patent No. 07182965 JP A, and No. 09139171 JP A. This method employs a nickel alloy containing approximately 18-20 wt % of chrome, and a reductive material, for blackening a cathode sleeve at approximately 1050xc2x0 C. for 1 to 2 minutes in a moisturized hydrogen atmosphere to form chrome oxide. Then, the blackened cathode sleeve is heat treated in a dried hydrogen atmosphere to reduce an outer wall of the oxidized cathode sleeve. These blackening/reducing treatments, as illustrated in FIG. 2B, provide the inside surface 20a of the sleeve with little surface porosity and approximately 32 wt % chrome and a radiation ratio of approximately 0.65 to shorten the picture presentation time lag. The outside surface 20b has approximately 26 wt % of chrome and an approximate 0.32 radiation ratio, thereby serving to reduce the heat loss of the heater.
However, the foregoing method is expensive as the fabrication process is complicated due to the two blackening/reducing heat treatments. Additionally, second reduction heat treatment of this related art fabrication process causes the heat radiation ratio of the inside surface 20a of the sleeve of the cathode to possibly be reduced. The fabrication method also has difficulty in controlling degrees of the blackening/reducing the inside and outside surfaces of the cathode sleeve in the blackening/reducing heat treatments.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
Accordingly, the present invention is directed to a cathode in a CRT that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a cathode in a CRT which can reduce a heater power consumption and shorten a picture presentation time lag.
Another object of the present invention is to provide a cathode in a cathode ray tube which includes an emission layer at an upper part of the cathode, and a sleeve for inserting a heater therein, wherein the sleeve contains a blackened material that has a porous surface.
Another object of the present invention is to provide a cathode in a CRT including, an emission layer at an upper part of the cathode, a sleeve on side portions of the cathode, and a heater within the cathode, wherein the sleeve has a porous surface formed by heat treating a metal alloy in a moisturized hydrogen atmosphere to blacken the metal alloy, and vaporizing the blackened metal alloy to form the porous surface.
Another object of the present invention is to provide a method of forming a cathode in a cathode ray tube including forming a cathode which include an emission layer, a heater and a sleeve, then heat treating the sleeve, and vaporizing the sleeve to form pores in the surface of the sleeve.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.